Hamburger and Hamilton - Summa gallicana

DEVELOPMENTAL DYNAMICS 195231-272 (1992) 

Reprinted from the JOURNAL OF MORPEOLOCY 

Vol. 88, No. 1, January 1951 

A SERIES OF NORMAL STAGES IN THE 

DEVELOPMENT OF THE 

CHICK EMBRYO 

VIKTOR HAMBURGER 

Department of Zoology, Washington University, St. Louis, Nissouri 

HOWARD L. HAMILTON 

Department of Zoolo8gy and Entom2070gy, Iowa State College, Ames 

FORTY-FIVE FIGURES 

The preparation of a series of normal stages of the chick 

embryo does not need justification at a time when chick ernbryos 

are not only widely used in descriptive and experimental 

embryology but are proving to be increasingly 

valuable in medical research, as in work on viruses and cancer. 

The present series was planned in connection with the 

preparation of a new edition of Lillie’s DeueZopmerzt of the 

Chick by the junior author. It is being published separately 

to make it accessible immediately to a large group of workers. 

Ever since Aristotle “discovered” the chick embryo as the 

ideal, object for embryological studies, the embryos have been 

described in terms of the length of time of incubation, and 

this arbitrary method is still in general use, except for the 

first three days of incubation during which more detailed 

characteristics such as the numbers of somites are applied. 

The shortcomings of a classification based on chronological 

age are obvious to every worker in this field, for enormous 

variations may occur in embryos even though all eggs in a 

setting are plmaced in the incubator at the same time. Many 

factors are responsible for the lack of correlation between 

chronological and structural age. Among these are : genetic 

differences in the rate of development of different breccls 

(eg., the embryo of the White Leghorn breed develops more 

49 

Address renrint reauests to Dr. Joshua R. Sanes. DeDartment of 

Anatomy and Neurobiology, Washington University’ Medical School, 

St. Louis, MO 63110. 

Q 1993 WILEY-LISS, INC.

232 HAMBURGER AND HAMILTON 

50 V. HAMBURGER AND H. L. HAMILTON 

rapidly than that of the Barred Plymouth Rock and hatches 

approximately a day earlier) ; seasonal differences in the 

viability and vigor of embryos; differences in the stage of 

development when incubation is started ; differences in the 

“freshness” of eggs, Le., the lapse of time between laying 

and incubation; differences in the temperature of eggs when 

placed in the incubator, and in the size of individual eggs; 

differences in the temperature of incubation, and in type and 

size of incubator. 

The wide variations in external form which occur at any 

given chronological age are clearly seen in tables 1 and 2 

which show the distribution of 296 embryos from the 4th day 

until hatching when classified according to our series of 

stages. For example, a “6-day” embryo may range anywhere 

from stage 27 + to stage 31 (table 1). It will also be noted that 

the data in table 1 are based on an incubation-temperature of 

103°F. (ca. 39.4”C.) whereas those in table 2 are based on 

a temperature of 375°C. This difference has resulted in the 

skipping of the “9-day” embryo altogether! It is not surprising, 

therefore, that the use of chronology with its lack of 

precision in the designation of embryos has actually led to 

misunderstandings and controversies which could readily 

have been avoided by the use of an adequate series of morphological 

stages. 

Keibel and Abraham (1900) worked out a series of stages 

of the chick embryo based on morphological characters. This 

series never became popular and it has been rarely used and 

quoted. Among its shortcomings are its inadequate illustrations 

which often make the identification of an embryo 

difficult, the incomplete coverage of older stages, and perhaps 

also the format and relative inaccessibility of the Normentafeln. 

M. Duval’s masterful Atlas d’EmbryoZo,gie (1889) with 

its artistically perfect drawings is unfortunately incomplete 

in that it does not go beyond the 8th day of incubation. 

Our own work covers the entire period of incubation. Its 

aim is to serve the practical purpose of identifying and designating 

embryos on the basis of external characters. The uii-

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NORMAL STAGES OF THE CHICK 

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52 V. HAMBURGER AND 13. L. IlAMILTON 

exc.ellec1 series of stages of Ainblystoma by Harrison lias 

served as a model. Our series is independent of chronological 

age and of size of embryos, as is the ,4?r&Zystoma series. The 

photographs and drawings show most of the diagnostic 

criteria ; this, we hope, will facilitate a rapid identification. 

A brief text is added, in which the distinguishing criteria are 

listed for each stage. 

We are aware of the complications which derive from the 

iiidepeiideiit variations of different characters. For instance, 

the progress of differentiation in the visceral arches may lag 

behind that in the limb-buds, when compared with an average 

sequence. For this reason, the amnion and allantois, and the 

iiuinber of pairs of somites beyond 22 are of no diagnostic 

value. We have tried to establish average or “standard” 

types by comparing a considerable number of embryos in each 

stage, aiid me have selected for illustrations those embryos 

which appeared typical. 

Dixi-iiig the different phases of development, different characters 

become prominent, and theref ore particularly useful 

for the diagnosis. For the second day of incubation we have 

adopted the conventional designation of embryos according 

to numbers of pairs of somites. We have chosen intervals of 

three somites as “stages”; this makes it possible to designate 

embryos with intermediate numbers of somites by a + 

or - sign. Somites mere not counted unless fully formed and 

coiiipletely separated by clefts from the adjacent mesoderm. 

The first somite was not included in the counts beyond stage 

10 when it begins to dwindle away. 

During the third day of incubation, or, more precisely, 

from the stage of 22 somites oiiwai-d (stage 14), the rapid 

progress in development of the limbs provides the most com 

venient diagnostic criteria. Preliminary \vork oii these stages 

has lieen done by Hamburger (’38, ’42) and by Saiinders 

(’48). Our stages 15 to 21 are identical with stages 1 to 7 of 

these authors. The original work was carefully rechecked 

and detailed descriptions of all characters were added. 

Stages 8 and 9 of Xawiders are combined in 0111’ stage 22;

NORMAL STUES OF THE CHICK 

235 

NORMAL STAGES OF THE CEICK 53 

stage 10 of Saunders is identical with our stage 23. The developmental 

phase between 4 and 9 days of incubation is 

characterized by rapid changes in the wings, legs, and visceral 

arches. From the 8th to the 12th days, feather-germs and 

eyelids provide the most useful criteria. The designation of 

stages during the last phase of incubation is difficult because 

practically no new structures are formed and there is mainly 

just growth of what almready exists. Hence, we have had to 

make use of measurements of the lengths of the beak and of 

the toes. 

The senior author is responsible for stages 14 to 35 and the 

junior author for all the others. 

All illustrations and descriptions are based on material 

fixed in Bouin's solution or formalin. It is possible that 

minor distortions have occurred due to differential shrinkage, 

for instance in the amnion. The embryos used for stages 

14 to 35 came from a flock of White Leghorns at St. Louis. 

They were incubated in a small size Buckeye incubator (for 

350 eggs) without forced draft, at a temperature of 1Q3"F. 

(ca. 39.4"C.). The embryos used for the other stages were 

of several breeds (White Leghorn, Barred Plymouth Rock, 

and Rhode Island Red) from the Iowa State College Poultry 

Farm, and were incubated in a forced-draft incubator at a 

constant temperature of 375°C. During the course of this 

work several hundred embryos have been examined and classified 

from the second day of incubation until hatching. 

We wish to express our great appreciation of the expert 

advice and help which Dr. Mary E. Rawles, Johns Hopkins 

University, and Dr. Nelson T. Spratt, University of Minnesota, 

have given us in the difficult matter of selecting stages 

1 to 6. Dr. Rawles has generously supplied data on the range 

of time within which a given stage may usually be obtained, 

based on records of 7 0 embryos incubated at 38°C. Her 

data are included iii the text for stages 5-14 and 22. Dr. 

Spratt has supplied photographs and slides for illustrating


54 V. HSMBUKGEB AND H. L. HAMILTON 

the prc-somitie stages and has given estimates of incubationtime 

for stages 2-4. 

The photographic work for stages 22 to 35 was done by Mr. 

L. Pinkers and Mr. D. Bucklin at Washington University, and 

that for the remaining stages by Mi-. John Staby of the Iowa 

State College Experiment Station. All drawings were made 

by Mix. Elsie Herbold Froeschner of Ames, Iowa. Additional 

assistance was given by Miss Thelma Dunnebacke and lzliss 

Mary Lee Winkler, both of Washington University. We wish 

to thank all our helpers for their efficient and h inti ring cooperation. 

The work was supported, in part, by a Research 

Grant of the Rockefel’ler Foundation to the Department 

of Zoiilogy of Washington University, and by the Industrial 

Science Research Institute of Iowa State College. 

The description which follows should be used in conjunction 

with the ill’ustrations (plates 1-14) which are numbered 

according to stages. 

Xiage I. Pre-Streak: Prior to the appearance of the primitive 

streak. An “embryonic shield” may be visible, due to the accumulation 

of cells toward thc posterior half of the blastoderm. 

(See Spratt, ’42, pp. 71-72.) 

Rtage 2. Initial Streak: (‘( Short-Sroad beginning-streak” of Spratt, 

’42). A rather transitory stage in which the primitke streak 

first appears as a short, conical thickening, almost as broad as 

long (0.3-0.5 mm in length), at the posterior border of the 

pellucid area. Usually obtained after 6-7 hours of incubation. 

Sfage 3. Intermediate Xtreak: (12-13 hrs.). The primitive streak 

extends from the posterior margin to approximately the center 

of the pellucid area. The streak is relatively broad throughout 

its length, and is flared out where it touches the opaque area. No 

primitive groove. 

Stage 4. Definitive Xtreak: (18-19 hrs.). The primitive streak has 

reached its maximal length (average length = 1.88 mm, Spratt, 

’46). The primitive groove, primitive pit, and Hensen’s node are 

present. The area pellucida has become pear-shaped and the 

streak extends over two-thirds to three-fourths of its length. 

Stage 5. Head-Process: (19-22 hrs.). The notochord or headprocess 

is visible as a rod of condensed mesoderm extending


237 

NORMAL STAGES OF TEE CHICK 55 

forward from the anterior edge of Hensen’s node. The head-fold 

has not yet appeared. Since the length of the notochord increases 

during this stage, it is suggested that the length of the notochord 

in millimeters be appended to the number of the stage for further 

precision (e.g., “Stage 5-0.2” would designate a notochordal 

blastoderm with notochord 0.2 mm in length). 

Btage 6. HeabPold: (23-25 hrs.). A definite fold of the blastoderm 

anterior to the notochord now marks the anterior end of the 

embryo proper. No somites have yet appeared in the mesoderin 

lateral to the notochord. This is a transitory stage, since the 

head-fold and the first pair of somites develop rather clos~ly in 

time. 

Stages 7 to 14 are based primarily on the numbers of pairs of 

somites which are clearly visible. The number of somites appears to 

be the simplest criterion for staging this phase of development, and 

it is sufficiently accurate for practical purposes. A stage is assigned 

to every third pair of somites which is added; embryos with inbetween 

numbers of somites are designated by adding a + or - 

sign to the appropriate stage. Thus, stage 7 designates an embryo 

with one pair of somites; stage 7 + = two pairs; stage 8 - = three 

pairs; stage 8 = four pairs; etc. (See plates 2 and 3.) 

Stage 7. One somite: (23-26 hrs.). This is actually the second 

somite of the series; number one is not yet clearly defined. 

Neural folds are visible in the region of the head. 

Stage 8. Pour somaites: (26-29 hrs.). Neural folds meet at level 

of midbrain. Blood-islands are present in posterior half of 

blastoderm. 

Stage 9. Seven. somites: (29-33 hrs.). Primary optic vesicles are 

present,. Paired primordia of heart begin to fuse. 

Stage 10. Ten somites: (33-38 hrs.). The first somite is becoming 

dispersed ; it is not included in the counts far subsequent stages.’ 

First indication of cranial flexure. Three primary brain-vesicles 

are clearly visible. Optic vesicles not constricted at bases. Heart 

bent slightly to right. 

Stage 11. Tlawteen somites: (4045 hrs.) Slight cranial flexarr 

Five nenronieres of hindbrain are distinct. Anterior neuropore 

is closing. Optic vesicles are constricted at bases. Heart bent 

to right. 

’ It is suggested that embryos which haye gained oiie soiiiite beyond Stage 10, 

but have lost s. 1 in the meantime, be designated as Stage 10 2; Stage 10 + 

would then Itale 11 s., not counting the rudimentaiy one; stage 11 - = 12 s., not 

couiitiiig the rudimentary one, etc.

238 

56 V. HAMBURGER AND H. L. HAMILTON 

Xtage 12. Sixteen somites: (45-49 hrs.). Head is turning onto left 

side. Anterior nenropore closeil. Telencephalon indicated. Primary 

optic vesicles and optic stalk well established. Auditory 

pit is deep, but wide open. Heart is slightly S-shaped. Headfold 

of amnion covers entire region of forebrain. 

Stage 13. Nineteen somites: (48-52 hrs.). Head is partly to fully 

turned to the left. Cranial and cervical flexures make broad 

cnrves. Distinct enlargement of telencephalon. Slight narrowing 

of opening to deep auditory pit. No indication of hppophysis. 

Atrio-ventricular canal indicated by constriction. 

Head-fold of amnion covers forebrain, midbrain, and anterior 

part of hindbrain. 

Siage 14. Twenty-two ~sowites: (50-53 hra.). 

Flexures aad rotatim. Cranial flexure: axes of forebrain and 

hindbrain form abont a right angle. Cervical flexure a broad 

curve. Rotation of body back as far as somites 7-9. Behind 

this level, a slight flexure makes its appearance which will be 

referred to as “trunk-flexure.” 

T7isceral arches 1 and 2, and clefts 1 and 2 are distinct. Posterior 

arches not distinct. 

Primary optic vesicle begins to invaginate ; lens-placode is 

formed. Opening of nuatory pit constricted. Ratkke’s pouch 

can be recognized. Ventricular loop of heart now ventral to 

atrio-ventricular canal. Anamhz extends to somites 7-10. 

Beyond stage 14 the number of somites becomes increasingly 

difficult to determine with accuracy. This is due in port to the dispersal 

of the mesoderm of the anteriormost somites, and, in later 

stages, to the curvature of the tail. Total somite-counts given for 

the following stages are typical, but sufficiently variable m as not to 

be diagnostic. For these reasons, the limb-buds, visceral arches, and 

other externally visible structures are used as identifying criteria 

from stage 15 onward. 

Stage 15. (Hamburger, ’38; Sannders, ’48, stage 1 ; ca. 50-55 hrs.) . 

1. Lateral body-folds extend to anterior end of wing-level 

(somites 15-17). 

2. Limb-prinaordia: prospective limb-areas flat, not yet demarcated. 

Inconspicuous condensation of mesoderm in wing-level. 

3. Smaites: 24-27. 

4. Amnion extends to somites 7-14. 

5. Flexures and rotatiom. Cranial flexure: axes of forebrain 

and hindbrain form an acute angle. The ventral contours of 

forebrain and hindbrain are nearly parallel. Cervical flexure


239 


a broad curve. The trunk is distinct. Rotation extends to 

somites 11 to 13. 

6. V%soeral arches: Visceral arch 3 and cleft 3 are distinct. 

The latter is shorter than cleft 2 and usually oval in shape. 

7. Eye: Optic cup is completely formed; double contour distinct 

in region of iris. 

Stage 16. (Hamburger-Sannders stage 2 ; ca. 51-56 hrs.). 

1. 

Lateral body-folds extend to somites 17-20, between levels 

of wings and legs. 

Limbs. Wing is lifted off blastoderm by infolding of lateral 

2. 

body-fold. It is represented by a thickened ridge. Primordinm 

of leg is. still flat; represented by a condensation of niesoderm. 

3. flomites: 26-28. 

4. Amnion extends to somites 10-18. 

5. Plexures and rotaiion: All flexures are more accentiiated 

than in stage 15. Rotation extends to somites 14-15. 

6. Tail-bwd a short, straight cone, delimited from blastoderm. 

7. Vislceral arches: Third cleft still oval in shape. 

8. Forebrain lengthened ; constrictions between brain-parts are 

deepened. Epiphysis indistinct or not yet formed. 

Xtage 17. (Hamburger-Saunders stage 3 ; ca. 52-64 hrs.). 

1. Lateral body-folds extend around the entire circumference 

of the body. 

2. Limb-buds: both wing- and leg-buds lifted off blastoderill 

by infolding of the body-folds. Both are distinct swellings of 

approximately equal size (see plate 5). 

3. Xomdtes: 29-32 

4. Amnion: Considerable variability, ranging from a condition 

in which posterior trunk and tail, from approximately somite 

26, are uncovered, to complete closure except for an oval hole 

over somites 28-36. Intermediate stages with an anterior fold 

covering as far back as somite 25 and a posterior fold 

covering part of the tail are common. 

5. Plextcres and rotation: Cranial flexure is unchanged. Cervical 

flexure is more sharply bent than in preceding stages, 

but its angle is still larger than 90". Trunk-flexure is distinct 

in brachial level. Rotation extends to somites 17-18. 

6. Tad-bud bent ventrad. Its mesodern1 unsegmented. 

7. Epiphysis: a distinct knob. Indication of nasal pzts. 

8. Allantois: not yet formed.

240 HAMBURGERANDHAMILTON 

58 V. HAMBURGEE AND H. L. HA1\!tILTON 

Stage 28. (Haiiiburger-Sa~iiider stage 4; ca. 65-69 hrs.). 

1. Linab-B~ls enlarged ; leg-buds slightly larger than wing-buds 

(see plates 4 and 5). L/W of wing = 6 or < 6 (L = length = 

anterior-posterior dimension as measured along the body-wall ; 

W = width = distance from body-wall to apex; see stage 20, 

plate 3). 

2. Xomites: 30-36; extend beyond level of leg-bud. 

3. Amnion: Usually closed; occasionally an oval hole in lumbar 

region. 

4. Flexures and rstation: At the cervical flexure, the axis of 

the medulla forms approximately a right angle to the axis of 

the posterior trunli. The trunk-flexure has shifteldl to the 

lumbar region. The rotation extends now to the posterior part 

of the body ; hence, the leg-buds are no longer in the horizontal 

plane. 

5. The tail-Dud is turned to the right, at about an angle of 

90” to the axis of the posterior trunk. 

6. Visceral arches: Maxillary process absent or inconspicuous. 

Fourth visceral cleft indistinct or absent. 

‘7. Allamtois: A short, thicli-walled pocket ; not yet vesicular. 

(Hamburger-Saunders stage 5 ; ca: 68- 72 hrs.). 

1. Linab-buds: Enlarged, symmetrical. Leg-buds slightly larger 

and bulkier than wing-buds (see plate 5). L/W of wing- 

Sfage 19. 

2. 

3. 

4 

5 

buds = 4-6. 

Sonaites: 3740; extend into tail; but the end of the tail 

which is directed forward is unsegmented. 

Flexup-es and rotation: In the cervical flexure the axis of the 

medulla forms an acute angle with the axis of the trunk. The 

trunk-flexure has nearly or entirely disappeared due to the 

rotation of the entire body. The contour of the posterior part 

of the trunk is straight to the base of the tail. 

Tad-b~d curved, its tip pointing forward. 

Tizsce~-al arches: The maxillary process is a distinct swelling 

of approximately the same length as the mandibular process. 

The first visceral cleft is an open narrow slit at its dorsal 

part. It continues into a ‘shallow furrow. The second arch 

projects slightly over the surface. The 4th cleft is a fairly 

distinct slit at its dorsal part and continues ventrally as a 

shallow groove. It does not perforate into the pharynx as a 

true (open) cleft, but is, nevertheless, IiomoiogoLis to the other 

three clefts. 

6. Allantois: A small pocket of variable size; not yet vesicular. 

‘7. Eyes unpigmentecl.


241 

NOlX1RIAL STAGES OF THE CHICK 59 

Stage 20. (Hamburger-Saunders stage 6 ; ca. 70 - 72 hrs.) . 

1. LimB-buds enlarged ; leg-buds are (distinctly larger from no~v 

on than wing-buds. The wing-buds are still approximately 

symmetrical ; the leg-buds are slightly asymmetrical (see plate 

5). L/W of wing = 3-3.9 ; L/W of leg = 3-2.3. 

2. Somites: 40-43 ; tip of tail still unsegmented. 

3. Flexures and rotation: Cervical flexure more accentuated 

than in stage 19. The bend in the tail-region begins to extend 

forward into the lunibo-sacral region. Contour of mid-trunk a 

straight line. Rotation completed. 

4. Visceral arches: Maxillary process distinct, equals or exceeds 

the mandibular process in length. Second arch projects 

over surface. Fourth arch less prominent and smaller than 

third arch. Fourth cleft shorter than third cleft; a narrow 

slit at its dorsal part, continuing into a shallow groove. 

5. Allantois: Vesicular, variable in size; 011 the average of the 

size of the midbrain. 

6. Eye-pigment. A faint grayish hue. 

Stage 21. 

(Saunders stage 7 ; ca. 34 days). 

1. Linzbs: Enlarged; both wing- and leg-buds are slightly 

asymmetrical ; their proximo-distal axes are directed caudad, 

and the apex of the bud lies posterior to the midline bisecting 

the base of the bud. The posterior contours of wing- and 

leg-buds are steeper than the anterior contours; they meet the 

baseline at an angle of approximately 90". L/W of wing = 

2.3-2.7; L/W of leg = 2.0-2.5. 

2. Somztes: 43-44; extreme tip of tail unsegmented. 

3. Flexures: The posterior c-urvatore includes the lumbo-sacral 

region. The dorsal contour of the trunk is straight or slightly 

bent. 

4. Visceral arches: Maxillary process is defiiiitely longer than 

5. 

mandibular process, extending approximately to the middle 

of the eye. The second arch extends distinctly over the surface 

and overlaps the third arch ventrally. Fourth arch 

distinot; 4th cleft visible as a slit. 

Alla?ztois: Variable, usually larger than in stage 20; may 

extend to head. 

6. Eye-pigmentation: Faint. 

Stage 22. (Saunders stages 8 and 9 combined ; ca. 34 days). 

1. Linzbs: Elongated buds, pointing caudad. The anterior and 

posterior contours are nearly parallel at their bases (see 

plate 7). L/W of wing = 1.5-2; L/W of leg = 1.3-1.8.


60 V. TIAMBURGER AND H. L. HAMILTON 

2. Sondes: Extend to tip of tail. 

3. Plexures: Little change. The dorsal contour of the trunk is 

a straight line or curved. 

4. Visceral arches: Little change compared with stage 21. 

Maxillary process enlarged; 4th cleft distinct as a slit. 

5. Allantois: Variable in size; extends to head and may overlap 

the forebrain. 

6. Eye-pigmentcrtion: Distinct. 

Stage 23. (Saunders stage 10 ; ca. 3+ 4 days). 

1. 

Limbs: Longer than in stage 22; particularly the proximal 

parts in which anterior and posterior contours run parallel 

are lengthened ; otherwise, little change in shape. Both wing- 

and leg-buds approximately as long as they are wide. 

Visceral arches (see plates 7 and 8) : Maxillary process is 

2. 

lengthened further. The first visceral cleft is represented by a 

broken line. Its dorsal part is a distinct slit. A slight protuberance 

(“a’,) is noticeable anterior to the dorsal slit. The claudal 

part of the second arch is distinctly elevated over the surface. 

Arches 3 and 4 are still completely exposed. Visceral cleft 3 is 

a distinct groove, and cleft 4 is reduced to a narrow oval pit at 

its dorsal end. 

3. Flexures: The dorsal contour from hindbrain to tail is a 

curved line. 

Stage 24. 

(ca. 4 days). 

1. Limbs: Wing- and leg-buds distinctly longer than wide. 

Digital plate in wing not yet demarcated. Toe-plate in leg-bud 

2. 

Staye 25. 

distinct. Toes not yet demarcated. 

Visceral arches (see plates 7 and 8) : First visceral cleft a 

distinct curved line. Slight intdication of two protuberances 

(‘‘ a, ” “b’ ’) on mandibular process and of three protuberances 

(l,,,,, C L e , ” C l f , , ) 

on second arch. Part “c” of mandibular 

process is receding. Second arch longer ventrally (at “f ’,) and 

much wider than mandibular process. Third arch reduced and 

partly overgrown by second arch; 4th arch flattened. Both are 

sunk beneath the surface. Thirld visceral cleft is an elongated 

groove. Fourth visceral cleft reduced to a siiiall pit. 

(ca. 4t days). 

1. Liinibs: Elbow and knee-joints distinct (in dorsal or ventral 

view). Digital plate in wing distinct, but no demarcation of 

digits. Indication of faint grooves demarcating the third toe 

on leg. 

2. Visceral al-ches (see plates 7 and 8) : Maxillary process lengthened; 

it meets the wall of the nasal groove (notice the notch at


point of fusion). Three protuberances on each side of first visceral 

cleft (“a” to “f”). In dorsal view, “a,” “b,” and “d” 

appear as round knobs, and c1c77 as a flat ridge. Part “f” is 

conspicuous and projects distinctly over the surface. It mill be 

referred to as the “collar.” Dorsal part of third arch still 

visible. Third and 4th visceral clefts reduced to small circular 

pits. 

Stage 26. (ca. 43-5 days). 

1. Limbs: Considerably lengthened. Contour of digital plate 

rounded. Indication of faint groove between second and 

third digit. Demarcation of the first three toes distinct. 

2. Visceral nrrhps (see plates 8 and 9) : Contour of maxillary 

process a broken line. Mandibular process lengthened ventrally. 

Protuberances “a” and “b” project over the surface. The 

middle protuberance (11 b”) is subdivided by a shallow groove. 

A small knob is distinct at the dorsal edge of l1 c. ” On the second 

arch, protuberances l1 d” and “e” are only slightly elevated 

over the surfaoe. The (“f”) has broadened and overgrown 

visceral arches I11 and IV. A deep groove separates 

“f” from “c.” The two pits represent,ing the 3rd and 4th 

visceral clefts are no longer visible. 

Stage 27. 

(ca. 5 days). 

1. Limbs: Contour of digital plate angular in region o€ first 

digit. Grooves between first, second, and third digits indicated. 

Grooves between toes are distinct on outer and inner 

surfaces of toe-plate. First toe projects over the tibia1 part 

2. 

at an obtuse angle. Tip of third toe not yet pointed. 

Visceral at-ches (see plates 8 and 9) : Contour of maxillary 

process is a curved, broken line. Mandibular process has broadened 

ventrally (at “c”) and grown forward. Protuberances 

“a” and “b” project over the surface. Parts “d” and “e” 

are flat. Protuberances “b” and “e” are close to fusion, but a 

separating line is still distinct. The ‘‘ collar” (‘ ‘ f ’’) has broadened 

and continned its growth backward. It rises conspicuously 

above the surface. The groove between “c” and “f” has 

w i deiic d 

3. Beak: Barely recognizable. 

Sfage 28. (ca. 56 days). 

1. Limbs: Second digit and third toe longer than others, which 

gives the digital and toe-plates a pointed contour. Three 

digits and 4 toes distinct. No indication of 5th toe. 

2. Visceral arclzes (see plates 8 and 9) : Protnberance “a” still 

projects over the surface. Mandibular process has lengthened


62 T7. HAMBURGER AND JT. L. HAMILTON 

and grown forward. Parts “b” and “err have fused; a fine 

suture line is occasionally still visible. Parts “b,” “d,” and 

“e” no longer project above the surface. External auditory 

opening is now very distinct between “a,” “b,” and “d.” 

l1 Collar ’? 

(‘‘ f ”) projects distinctly over the surface. The neck 

between “collar” and mandible has lrngthenril 

3. Beak: A distinct outgrowth is visible in profile. 

Stage 29. (aa. 6 days). 

1. Limbs: Wing bent in elbow. Second digit distinctly longer 

than the others. Shallow grooves between first, second, and 

third digits. Second to 4th toes stand out as ridges separatrd 

by distinct grooves, and u. ith iiidiclations of webs between 

them. Distal contours of w3bs are straight lines, occasionally 

with indication of convexity. Rudiment of 5th toe visible. 

2. Visceral arches: Mandib~ilar process lengthened (compare 

with stage 28). Mandibular process and secoiid arch are 

broadly fused. Auditory ineatus distinct at dorsal end of 

fusion. All protuberances have flattened. Neck between 

“collar 77 and mandibular process has lengthened. “Collar” 

stands out conspicuously. 

3. Beak: More prominent than in stage 28. No egg-tooth 

visible as yet. 

Stage 30. (ca. 64 days). 

1. Limbs: The threc major segments of wing and leg are 

clearly demarcated. Wing bent in elbow-joint. Leg bent in 

knee-joint. Distinct grooves between first and second digits. 

Contours of webs between first two digits and between all 

toes are slightly curved concave lines. 

2. Visceral arches : The mandibular process approaches the 

beak, but the gap between the two is still conspicuous. 

TJengthening of neck between l1 collar ’’ and mandible is very 

3. 

conspicuous. “ Collar’ begins to flatten. 

Feather-germs: Two dorsal rows to either side of the spinal 

cord at the brachial level. Three rows at the level of the 

legs; they are rather indistinct at thoracic level. None on 

thigh. 

4. Scleral papillae: One on either side of choroid fissure; soinetimes 

indistinct but never more than two. 

5. Egg-tooth distinct, slightly protruding. Beak more pronoanced 

than iii previous stage. 

Stagr 31. (ca.‘i 

days). 

1. Limbs: Indication of a web between first and secoiid digits. 

Rudinient of 5th toe still distinct.


2. 

3. 


Visceral arches: The gap between mandible and beak has 

narrowed to a small notch. “Collar” inconspicuous or absent. 

Peather-germs: On dorsal surface, continuous from brachial 

to lumbo-sacral level. Approximately 7 rows at limbo-sacral 

level. Distinct feather papillae on thigh. One indistinct row 

on each lateral edge of the tail. 

Xcleral papillae: Usually 6; 4 on the dorsal side near the 

4. 

choroid fissure, and two on the opposite side. 

Stage 32. (ca. ‘it days). 

1. Limbs: All digits and 4 toes have lengthened conspicuously. 

Rudiment of 5th toe has disappeared. Webs between digits and 

toes are thin and their contours are concave. Differences in 

2. 

size of individual digits and toes become conspicuous. 

Visceral arches: Anterior tip of mandible has reached the 

beak. “ Collar” has disappeared or is faintly recognizable. 

Peather-germs: Eleven rows or more on dorsal surface at 

3. 

level of the legs. One row on tail distinct, second row in- 

Idistinct. Scapular and flight feather-germs barely perceptible 

at optimal illumination or absent. 

4. Scleral papillae: Six to 8, in two groups; one group on 

dorsal and one on ventral side. Circle not yet closed. 


1. Limbs: Web on radial margin of arm and first digit becomes 

discernible. All digits and toes lengthened. 

2. Visceral arches: Mandible and neck have lengthened con- 

3. 

spicuously. (Compare the ventral contour of boldy, from heartregion, 

along neck to tip of mandible, in this and the preceding 

stages.) 

Peather-germs: Scapular and flight feather-germs not much 

advanced over stage 32. Tail: three rows distinct, the middle 

row considerably larger than the others. 

4. Scleral papillae: Thirteen, forming an almost complete 

circle, with gap for one missing papilla at a ventral point near 

the middle of the jaw. 

Stage 34. 

(ca. 8 (days). 

1. Limbs: Differential growth of second digit and third toe 

conspicuous. Contours of webs between digits and toes are 

2. 

3. 

concave and arched. 

Visceral arches: Lengthening of mandible and of neck con- 

tinues (see previous stage). 

Peather-germs: On scapula, on ventral side of neck, on pro- 

coracoid, and posterior (flight) edge of wing, feather-germs 

are visible under good illumination. Feather-germs next to

HAMBURGER AND HAMILTON 

64 T. HA1\4BURGER AXD H. L. HAMILTON 

dorsal midline, particularly at limbo-sacral level, extend 

slightly over surface when viewed in profile. Feather-germs 

on thigh protrude conspicuously. One roK on inner side of 

each eye. None around umbiIim.1 cord. 

4 Sclera-1 papillae: Thirteen or 14. 

5 Nictitating waenbbrane extends halfway between outer rim 

of eye (eyelid) and scleral papillae. 


1. Limbs: webs between digits and toes become inconspicuous. 

A transitory protuberance on the ulnar side of the second 

digit is probably a remnant of the web. Phalanges in toes are 

distinct. 

2 Visceral arch~s: Lengthening of beak continues. Compare 

the distance between the eye and the tip of the beak, in this 

and the preceding stages. 

3 Feather-germs: All are more conspicuous. Mid-dorsal line 

stands out distinctly in profile view. At least 4 rows on inner 

side of each eye. New appearance of feather-germs near midventral 

line, close to sternum, and extending to both sides of 

umbilical cord. 

4 Nictitating membrane has grown conspicuously and approaches 

the outer scleral papillae. Eyelids (external to nictitating 

membrane) have extended towards the beak and have 

began to overgrow the eye-ball. The circuniference of the eyelids 

has become ellipsoidal. 

Stage 36. 

(cal. 10 days). 

1. Limhs: Distal segments of both wing and leg are proportionately 

much longer. Length of third toe, from its tip to the 

middle of its metatarsal joint = 5.4 i- 0 3 mm. Tapering primordia 

of claws are just visible on termini of the toes and on 

digit 1 of the wing. Protuberance on posterior side of digit 

2 

3 

2 of wing is missing. 

Visceral arches: Primordium of the comb appears as a prominent 

ridge with slightly serrated edge along the dorsal midline 

of the beak. A horizontal groove (the “labial groove”) 

is clearly visible at the tip of the upper jaw, hut is barely 

indicated on the tip of the mandible. Nostril has narrowed to 

a slit. Length of beak from anterior aiigle of nostril to tip 

of bill = 2.5 nun. 

Feather-germs: Flight-feathers are conspicuous ; coverts are 

jubt visible in web of wing. Feather-germs now cover the tibiofihular 

portion of the leg. At least 9-10 rows of feather-germs 

between each upper eyelid and the dorsal midline. Sternal 

tracts prominent, with 3-4 rows on each side of ventral mid-


247 


line when counted in anterior part of sternum, merging into 

many rows around the umbilicus. 

4. EyeZids: Nictitating membrane covers anteriormost scleral 

papillae and approaches cornea. Lower lid has grown upward 

to level of cornea. Circumference of lids is a narrowing ellipse 

with its ventral edge flattened. 

Stage 37. 

(ca. 11 days). 

1. Lzmbs: Claws of toes are flattened laterally and curved ventrally 

; dorsal tips are opaque. indicating onset of cornification. 

Tip of claw on wing is also opaque. Pads on plantar surface 

of foot are conspicuous. Transverse ridges along the superior 

surfaoes of the metatarsus and phalanges are first indication 

2. 

3. 

of scales. Length of third toe = 7.4 & 0 3 mm. 

Visceral arches: Labial groove on mandible is now clearly 

marked off. The comb is more prominent and clearly serrated. 

Length of beak from anterior angle of nostril to tip of bill = 

3.0 mm. 

Feather-gei-ms: Much more numerous, and in most-advanced 

tracts (e.g., along back and on tail) elongated into long, 

much-tapered cones. External auditory meatus is nearly surrounded 

by feather-germs. Circumference of eyelids is bordered 

by a single row of just-visible primordia; none on 

remainder of lids. Sternal tracts contain 5-6 prominent rows 

when counted at anterior end of sternum. 

4. Eyelids: Nictitating inembrane has reached anterior edge 

of cornea. Upper lid has reached dorsal edge of cornea. Lower 

lid has covered one-third to one-half of cornea. Circumference 

of lids now bounds a much-narrowed and ventrally-flattened 

biconvex area 

Xfage 38. 

(ca. 12 days). 

1. 1,zwzbs: Primordia of scales are marked off over entire surface 

of leg; ridges have not 5-et grown out to overlap surface. 

Tips of toes show a ventral center of cornification as well as 

the more extensive dorsal one. Main plantar pad is ridged 

2. 

3. 

when seen in profile. Length of third toe = 8.4 i 0.3 mm. 

Visceral arches: Labial groove marlred off by a deep furrow 

at the end of each jaw. Length of beak from anterior angle of 

nostril to tip of bill = 3.1 mm. 

Feather-gernzs: Coverts of web of wing are beconiing coni- 

cal. External auditory meatus is surrounded by feather-germs. 

Sternum is covered with feather-germs except along midline. 

IJpper eyelid is covered with newlyformed feather-germs ; 

lower lid is naked except for 2-3 rows at its edge.


66 V. HAMBURGER AND H. L. IIAMILTON 

4. Eyelids: Lower lid covers two-thipds to three-fourths of 

cornea. Opening between lids is much reduced. 

Stage 39. (ca. 13 days). 

1. Limbs: Scales overlapping on superior surface of leg. Major 

pads of phalanges corered with papillae ; minor pads are 

smooth. Length of third toe = 9.8 f 0 3 mm. 

2. Visceral awhes: Mandible and maxilla cornified (opaque) 

back as far as level of proximal edge of “egg-tooth.” The 

channel of the auditory meatus can be seen only at the PO


NORMAL STAGES OF THZ CHICK 67 

2. Thiid toe: Length =18 6 I.0.8 mm. 

Stage 44. (ca. 18 days), 

1. Beak: Length from anterior angle of nostril to tip of upper 

bill = 5.7 mm. The translucent peridermal covering of the 

beak is starting to peel off proximally. 

2. Third toe: Length = 20 4 t 0.8 mm. 

Btage 45. (ca. 19-20 days). 

1. Beak: Length is no longer diagnostic; in fact, the beak is 

usually shorter than in stage 44, due to a loss (by sloughing 

off) of its entire peridermal covering. As a consequence, the 

beak is now shiny all over and more blunt at its tip. Both 

labial grooves have disappeared with the periderm. 

2. Third toe: Average length is essentially unchanged from 

that of stage 44, except in those breeds with a longer period of 

incubation (21 days) and a heavier build of body. For these 

latter, length of third toe = ca. 21.4 i 0.8 mm. 

3. Extra-embryonic membranes: Yolk-sac is half-enclosed in 

body-cavity. Chorio-allantoic membrane contains less blood 

and is “sticky” in the living embryo. 

Stage 46. Newly-hatched chick (20-21 days). 

REFERENCES 

DUVAL, MATHIAS 1889 Atlas d’Embryologie. (116 pp., 40 plates). Paris. 

HAMBURGER, VIKTOR 1938 Morphogenetic and axial self-differentiation of 

transplanted limb primordia of 2-day chick embryos. J. Exp. Zool., 

77: 379-399. 

1942 A Manual of Experiinental Embryology. 213 pp. University 

of Chicago Press. 

IIELBEL, F., AND K. ABRAHAM 1900 Normentaf el zur Entwicklungsgeschiclite 

des Huhnes (Gallus domesticus). 132 pp. Jena. 

SPRATT, NELSON T., JR. 1942 Location of organ-specific regions and their relationship 

to the development of the primitive streak in the early 

chick blastoderm. J. Exp. Zool., 89: 69-101. 

_~ 1946 Formcation of the primitive streak in the explanted chick 

blastoderm marked with carbon particles.. J. Exp. Zool., 103: 259- 

304. 

SAUNDERS, JOHN W., JR. 1948 The proximo-distal sequence of origin of the 

parts of the chick wing and the role of the ectoderm. J. Exp. Zool., 

108: 363403.

EXPLANATION OF PLATES 

All numbers in the following plates refer to the corresponding stage numbers in 

the text. The description of each stage should be consulted for a more complete 

explanation of the figures. 

PLATE 1 

EXPLANATION OF FIGURES 

Stages 1-3+, illustrated by photographs provided by Dr. Nelson T. Spratt, Jr. 

(Stages 1 and 2 are published in J. Exp. Zool., 103: 265 and 274.) X 20. 

68


251 

NOItMAL STAGES OF TJIE CHlCK 

V. HAMBURGER AND 1%. L. HAAIILTON 

PLATE 1


PLATE 2 

IIXPLANATION OF FJCr1JRF.S 

Stages 4-9! x 20. Stage 10, x 1%. (Stages -L> 5, aiid 8- were pliotographed froin 

slides provided by Dr. Nelson 7'. Rpratt,, .Ti,. All otlievs nre froill the Iowa State 

College collec.tion.)


I’l,i\TK 3 

ESPLAXATIOX OF FIGDRliS 

Stagcs 11-14, X I!. 

74


PLATE 3 

75


PLATE 4 

EXPLANAlION OF FIGURES 

Stages 15-18, x 12. Contours of limbs for stages 17 and 18 are shown in the 

drawings on plate 5. 

76


PLATE 4

...I./. 

258 


PLATE 5 

WINGS 

LEGS 

;) .:. 1 

.. 

i: 

...... 

j 

, 

. ... 

.i: 

.;;. 

.... 

. ::. 

. ,,,., 

.;. ... 2,. 

.:) 

STAGE 17 

...','. 

...... . 

.,. ..I,... 

STAGE 18 

...... 

.: .:>'. ..:., 

..... 

') 

. . 

...... ..:. 

:;::i:l: 

.....:I. 

:,. 

..... 

...... 

.I.' 

....... 

...... 

t:.:. : I: 

. ,.:*: 

........ ...:-. 

.._. 

....: >. 

.. .:i 

.: jj.; 

.;.::$p 

,..cx 

...!..?


259 

NORRIAL STAGES OF TI-IE CIIICli 

\,. HAXULRGIR 4XD H. L. II\lII,TON 

Stages 19-21 (clenied embiyos), X 12. Stage 21 (olxtq~te)), X 8, nit11 contours of linibs 

slio\vn in the clruwiilys below, ca. X 12.


I’1,AT‘d 

E M ’ T A N AT1 0 f; 0 L” 

i 

PIG I’ KE S 

x S. Tlic limbs for stage 22 are tlr:lwi1igs, cn. x 12; all others 

Stages 22-25, 

are pliotograplis, x 8. E’or details of visceunl arclics of stages 23-25, see plate 8. 

80


PLATE 7 

81


1'1-ATE 8 

Drawings of the region of the visceral arclies, iiiade from camera lueida tracings. Stages 

23-25, x 7. Stages 26-28, X 4.2. I-IV = visceral arches; mx., md. = maxillary and manrlibular 

processes of visceral arch I; 4 = 4th visceral cleft. see text for explallation of letters a-f. 

82


263 


V. HAMBURGER AND H. L. HAMILTON 

PLATE 9 

Stage 26, embryo and limbs, X 8. Stages 27-28, x 5. 

83


PLATE 10 

EXPLANATION OF FIGURES 

Stages 29-30, X 5. Stages 31-32, x 4. 

84


265 

NOIZMA4L STAGES OF. TIIE CHICK 

V. HIMBLRGER AXD H. L. HAHILTON 

PLATE 10 

85

266 HAMBURGER AND HAMILTON


87

268 HAMBUFtGERAND HAMILTON 

I’TATI? 12


269 

NORMAL STBGES OF THE CIIICK 

V. IXAMBURUBR .4XD H. L. IIAALILTON 

PLATE 12 

Rtnges 36-39, X 2. 

A9

270 


NORMAI, STAGES OF THE ('IIICK 

V. HAMH~RGLR 

AND H I H~MIIITON 

PLATE 13 

00


271 


V. HAMBURGEX AND 71, L. HAMIMTON 

PLATE 13 

Stages 40-43, x I$. The white arrows on the leg of stage 42 indicate the points between 

which mensurenients are made to determine the leiigth of the third (longest) toe in stages 36-45. 

91


92

Hamburger and Hamilton - Summa gallicana

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